Forming apparatus



une ze, 1956 A. P. HGGINS ETAL l' 2,751,871

FORMING APPARATUS 'oil I@ +4/I G INVENTORS:

ar/and @.ordon By Alfred P. Higgins ifa.

FGRMING APPARATUS Aifred P; Higgins and Garland R. Gordon, Fort Worth,

Tex., assignors, by mesne assignments, to General Dynamics Corporation, a corporation of Delaware Application October 11, 1951, SerialNo. 250,906 4 claims. (cl. 11s- 44) This invention relatesA toV apparatus adapted for use inA conjunction with a press for shape-forming sheet metal orV other materials, of the general type in which the Work piece is shaped over a male punch by means of a restrained rubber element serving as a female die.

In sheet metal die forming'of this general type, the conventional rigid female die, which is normally adapted to fit`over the punch to shape the nwork piece between the twoY elements, has been replaced with a resilient pad or bag, made usually of rubber, which is restrained laterally. When this resilient former is pressed down over the punch by the press with the work piece interposed between, the resilient material thereof conforms the work piece progressively over thepunchA to obtain the desired shape. That portion of the; work piece vremaining the plane of the original blank during anyv stage of the forming stroke or operation is known as the draw ring,

VOne important objective of the present invention is to provide metal shaping apparatus utilizing a resilient female die having an improved construction whereby the draw ring of the work piece is subjected to a restraining pressure against the forming of the resilient female die, which restraining pressure is controlled and independent of the main working pressure created by kthe press between the punch and the female die element. By affording a restraining pressure of this nature for the draw ring the ow of the metal, or other material, of the work piece may be controlled during the forming operation in order to prevent and eliminate wrinkles, avoid tearing of the work piece, and permit a deeper draw in a single operation. Y Y

Another object of the invention resides in providing in metal shaping apparatus of the above character a bolster plate having no dead, or unusable areas in its Working surface, and is unrestricted as to the size or shape of punches supported thereon within the limitations of the maximum area of the resilient female die.

A further object of the invention is to provide forming apparatus of this character including a bolster plate of such dimensions and supported solely at its edges in such a manner as to permit the use of substantially its entire surface for supporting one or more punches and being capable of withstanding the working pressure of the press substantially Without deflection.

Still another object of the invention is to provide a novel die apparatushaving a female die embodying a laterally restrained pad of compressible material and in` cluding a bolster plate of the above described characteristics, having associated means for transmitting an independent and controlled pressure to a pressure plate interposed between the bolster plate and the female die and adapted to operate in conjunction with the punch or punches, to restrain the draw ring of the work piece during the forming stroke.

A further object of the invention resides in providing a bolster plate as hereinabove described having a multiplicity of through bores so located that'controlled and independent pressure may be applied therethrough to the Friance 2 pressure plate: regardless of its shape or positioning thereof on the working area of the bolster.

A'further object of the invention is to provide dieforrning apparatus of this general character, in which the complexity and cost of the die-forming tools is reduced.

.Still another objective of the invention is to provide die-forming apparatus embodying a novel arrangement of parts wherein the working space between the operative parts can be more etiiciently utilized for simultaneously forming a' wide variety of shapes and sizes of blanks.

A still further object of the invention is to provide an improved construction for die-forming apparatus wherein a resilient female die member is adapted for'use with one or more male punch'members for simultaneously shaping a plurality of work pieces and including apressure pad surrounding the punches and adapted to exert restraining pressure against the draw rings 'of the work pieces, and having means for transmitting secondary and controlled pressure to the pressure pad, in such a manner that a variety of shapes and sizes of punches may be employed during a single operation in a simple and universally'adjustable'mannen Y Other objects of the' present invention will be readily apparent to those skilled in the art from the following specication andV drawings, in which like figures of reference denote vlike parts vthroughout the several views.

. ln the drawings:`v

Fig. l is a side elevation of one form of 4the die-formingv apparatus of the present invention illustrating therelationship of the different parts when mounted in a conventional press.

Fig. 2A is a plan view'of the bolster or punch-supporting means of the present invention in which a Vtypical lay-out of a plurality of punches is illustrated.

Fig. 3 is -a partial section of the present invention show ing the relationship of the work Vpieces or blanks, the tools, and the'forming apparatus at the start of an operation.

Fig. 4 is a similar section showing the relationship of these elements during or at the completion of the dieforming stroke. Y

The arrangement `shown and described herein constitutes a preferred embodiment, but it will be apparent that modifications may be made without departing from the;

spiritY and scope of the invention.

Referring toFig. l, the invention is shown mounted on the platens A and Bof a conventional press, preferably of the hydraulic type, but understood not to be restricted thereto in such manner that the'elements cooperate together for the die-forming operation as the platens A'and B are moved together. v s

As shown in the drawings, and having particular-reference to Figure 1, the die-forming apparatus of the present invention adapted for use with the conventional relatively movable platens A and B embodies adie-support 10 comprising a relatively thick body portion 11, preferably of rectangular shape, havingan upper surface 12 adapted to engage with movable platen A and a lower planar surface 13 which lies in opposition to platen B. Die-support 10 includes a peripheral flange 14 provided with holes to accommodate bolts 15 which cooperate with.

suitably Ylocatedtapped holesV in the lower surface of platen A to aix the `die-support 1t) to platen A.- A die member, indicated generallyrat 16, is located upon and supported from platen AA by die-support 10. Die member 16 comprises a generally rectangular box-like frame 17 having walls 18 and having an open central portion 21 defined by the inner surfaces of walls 18, Frame 17 includes laterally projecting external lugs 22 having holes therethrough `for the accommodation of bolts 23 which are adapted to fit Vsuitable tapped holes in die-support 10 to mount frame l17'upon lower planar surface 13 of platen A, wherein one end of the central portion 21 of frame 17 is closed by planar surface '13, and the other end opens toward platen B in assembly. A pad or block formed of compressible material, such as rubber or other yieldable material having the characteristics of rubber, which will have the capacity to deform in a manner to surround a body against which it is pressed, and having approximately the same dimensions, but somewhat less depth than central opening 2i of frame 17 is secured therein to effect a female die forming element, indicated Y in the drawings by the numeral 24, presenting a resilient die-forming Aface 2S ytoward the platen B.

Platen B is adapted to support one or more punch or die members, and the mounting structure therefor, for cooperation with the resilient die forming element 24 to shape such work pieces as are interposed therebetween when subjected to pressure by the movement of platen A toward platen B.

VIn theillustration of Figure l, but one punch, indicated at 26, is shown employed in the assembly. Punch 26 is but representative of punches that may be utilized and will comprise an upper surface 27, side walls 28 that conform to the interior dimensions of a part to be formed, and a planar lower surface 29.

interposed between punch 26 and resilient die forming yelement 24 in position to be shaped thereby is a work piece 31.

Cooperating with punch 26 and resilient die forming element 24'in the shaping of the work piece 31 is a pressure plate or pad 32 adapted to exert its pressure upon that portion of the work piece 31 known as the draw ring, which is indicated in the drawings by the numeral 33. Pressure plate 32 consists of a flat plate 34 having external dimensions that permit it to advance into central opening 21 and to tit closely adjacent the inner surfaces '4- of walls 18. Pressure plate 32 is providedV with one or more openings 35, the number of openings dependent upon the number of punches 26 employed, corresponding in size and shape to the transverse cross-section ofthe various punches 26, permitting the pressure pad 32 t0 Vbe moved axially with respect to the punch or punches 26.

The assembly or structure for supporting punch 26 and pressure plate 32 comprises a bolster plate 36, a base plate 37, a pair of support pedestals 38, a plurality of usual lluid actuator cylinders 41, a pressure plate 42, and a number of pressure transmitting rods or pins 43.

Bolster 36 preferably is of rectangular shape and has an upper planar surface 44 and a lower planar surface 45. The invention contemplates that bolster 36 shall be of suicient thickness to withstand the maximum work pressure of the press, exerted in the shaping of work pieces, substantially without deflection when supported solely at its edges.

Base plate 37 is likewise of a rectangular shape and conforms in outer dimensions to the bolster plate 36 and is adapted to lie upon and to be secured to the-upper surface 46 of platen B of the press, Bolster 36 is supported in spaced relation to base plate 37 kby the pedestals 3S, each of which, as shown, comprises a vertical web 47 having upper and lower lateral flanges 48 and 49 respectively. In assembly, the pair'of pedestals 38 are positioned adjacent opposite edges of the base plate 37 and bolster 36 with their flanges 48 and 49 extending outwardly. Bolts 50 are adapted to pass through aligned holes adjacent the edges of bolster 36 and upper flanges 48 and cooperate with nuts 51 toV secure the members oneto therother, and mounting bolts 52 are accommodated in aligned through-holes alorded in lower flanges 48 and base plate 37 and suitably tapped holes in upper surface 46 of platen B. The base plate 37 and pedestals 3S thus form a positive and stable means for supporting the bolster 36 by its opposite edges 53 and S4 and main` tainbolster 36 spaced from the platen B. It is noted that in this manner of mounting bolster 36 to platen B its centralportion Vdefined by the inner opposing edges of the apparatusrof the present invention.

55 and 56 of the pedestals 38 and the transverse free edges 57 and 53 of the bolster 36 is free and independent of support means. As stated hereinbefore, the thickness of bolster 36 Vis of an amount that it will withstand the force of the press maximum working pressure exerted overV an area conforming to that of the die-forming face of the resilient female die 24. No deflection will occur in bolster 36 such as would render it inoperative for the purpose for which it is designed. Although the pair of pedestals 38 illustrated are each of a width conforming to that of bolster 36 to afford a continuous support for its opposite edges 53 and 54 it is understood that the invention is not limited to but that number of pedestals and of that particular width. A plurality of pedestals of lesser widths could be substituted 'for each of the pair of pedestals 38 to support the opposite edges 53 and 54 of bolster 36. lt is preferred, however, that the cumulative widths of such plurality of pedestals be substantially equal in extent to the edges 53 and 54 to the purpose of affording a substantially continuous support therefor in order that the thickness of bolster 36 be of the same amount as when but two pedestals 38 are employed whereby the deflection is held within the working limits If the accumulative widths are less then it will be necessary t0 increase the thickness of bolster 36 to assure that allowable deflection will not be exceeded.

Further, it is contemplated that rather than supporting bolster 36 only at its lateral edges 53 and 54 pedestals would also be provided at transverseedges 57 and 58 to the end of effecting peripheral support of bolster 36. In such event, obviously the thickness of bolster 36 need not be as great as when but two edges are supported to achieve the strength required to permit bolster 36 to resist detrimental deflection under the force of the press working pressure.

The fluid actuating cylinders 41 are disposed in juxtaposed relation and suitably secured to the upper surface of base plate 37 in the area thereof between the pedestals 38. Each of the actuating cylinders 41 is conventional in construction comprising a stationary cylinder 62 and a movable piston or plunger 63 which is suitably actuated either hydraulically or pneumatically. The fluid actuating cylinders 41 are of conventional arrangement whereby the admission of fluid to the stationary cylinders 62 effects an extension of plungers 63, and withdrawal of such fluid results in their retraction. pose, all of the actuating cylinders 41 are interconnected by a network of branch pipes64 effecting communication between the cylinders 61. A common manifold 65 channels the fluid to branch pipes 64. A usual manually operable valve 66 controls the flow of lluid from a pressure source (not shown) to manifold 65. A regulatable pressure relief valve 67 of a conventional type is afforded in the fluid line in communication with cylinders 41 to maintain a predetermined pressure upon pressure plate 32 during the forming operation. Relief valve 67 connects to a reservoir, not shown. By this controlled admission or withdrawal of 'fluid under pressure to cylinders 41, simultaneous extension or restraction of all of the plungers 63 is afforded, as is a means for providing a controlled and independent restraining pressure upon the pressure plate 32.

The second pressure plate 42, which is utilized in the apparatus of the present invention, is generally rectangular in shape and of a width conforming to that of bolster 36, and is disposed in the area between bolster 36 and base plate 37 and the spaced pedestals 38. ln assembly, pressure plate 42 is adapted to beV supported upon the upper surfaces of the plungers 63 and is secured 'theretoV by means of machine screws 6G passing through suitably counterbored holes 68 in pressure plate 42 and into tapped holes 69 in the upper surface of plungers 63. It is thus apparent that the pressure plate 42 is adapted for reciprocaly movement toward and away from the For this purlower surface 45' of bolster 36 inresponseto :movement of the plungers 63. w' A im The portion of the bolster 36 dened by its transverse free edges 57 and 58 and the inner edges 55 and 56 of opposed pedestals 38 is provided substantially over its entire area with a multiplicity of rows of equally spaced holes 71, each successive row of holes being displaced by one-half the center distance between holes. The holes 71 extend through bolster 36 and serve to slidably accommodate the pressure transmitting rods or pins 43. Rods 43 are of equal length and have their lower ends supported in assembly upon the upper surface of pressure plate 42 which is subject to movement by actuating cylinders 61. Reciprocal movement of pressure plate 42 will thus result in reciprocal movement of pressure transmitting rods 43. Movement of rods 43 in response to upward movement of pressure plate 42 will project the upper extremities 72 of rods 43 above the upper surface 44 of bolster 36 to move draw ring clamping pressure plate 32 which, in assembly, is adapted to lie upon these upper extremities 72. TheV number of pressure transmitting rods 43 employed at'any time is dependent upon the size and shape of the' clamping pressure plate 32 being utilized. A suficient number is required that adequate support will be'provided throughout the area of the lower surface of clamping pressure plate 32 to maintain a horizontal position with respect to the upper surface 44 of boster 36 when spaced thereabove, and to assure that suicient clamping pressure is developed at the draw ring 33 of the work piece when the resilient female die 24 is pressed upon the draw ring on the movement of platen A toward platen B.

To support punch 26 upon the bolster 36 there is provided on the lower surface 29 of the punch ,one or more short pins or dowels 73 adapted to tinto holes. 71 ,ofl

bolster plate 36 to thereby locate the punch 26 on bolster 36 and to maintain its position with respect to the resilient female die member 24.

It is readily apparent that utilizing a bolster-plate 36 supported at its edges and having a multiplicity of holes 7?. disposed substantially throughout the entire unsupported area thereof makes such unsupported area available for the support of punching means, VThere are no dead areas as would be the case if a support were utilized for the bolster plate 36 other than at the ends. Since substantially the entire upper surface of'bolster 36 Vis available to support punches for the die forming operation, each job may be planned in such a manner as to obtain the greatest utilization of the apparatus, `by nesting and tting the punches 26 on the bolster 36 with respect to each other, the only limitation being that the punches lie within that area of the bolster 36 dened by the inner edges of the particular female die member 24 being used. As an example of the exibility of the present apparatus, the dot-dash line illustrations in Figure 2 represent a plurality of punches 26 arranged to make efficient use of the working area of bolster36.

lt is apparent that with the construction herein described tl'ie invention is unrestricted as to the size of parts to be formed except as limited by the forming area of the resilient female die 24. Further, a part of any conguration can be accommodated and shaped'by the invention, whether it be square, rectangular, circular, triangulanor of any other shape, symmetrical or unsymmetrical.

Parts of minimum size can also be shaped with? the present apparatus so long as the punchingmeans-can be supported upon bolster 36. -Y

It is to be noted that the method of supporting the bolster 36 permits the use of a rectangular shape therefor with consequent increase in the size of the punch supporting or work area. A rectangular shape is therefore to be preferred' over the conventional circular shaped bolster supported by a pedestal at its center. The size attainable by conventional circular shaped bolsters is gaat;

. Y 5 limited by reason of the usual press guide rods or posts upon which the movable platen reciprocates. Obviously no larger circular bolster can be utilized than can be fitted into the press in that areadened by the press guide posts.y The rectangular working area that can be included within the circumference of a circular bolster limited in its diameter by the placement of the press guide posts clearly cannot be equal to the working area of a rectangular bolster, of the type described herein, supported solely at its edges, and whose length is lnot defined by the press guide rods aorded for the platens.

The operation of the apparatus of the present invention will be described in connection with Figures 3 and 4.

Figure 3 illustrates the simultaneous use of two punches, which here are numbered 26a and 26b, for the shaping of two different parts. The punches 26a andV 26b are of the size and shape desired to be provided for the parts, and are located and maintained on bolster 36 by their dowels 73 which project into holes 71. The clamping pressure plate 32 has two openings 35a and 35b cut therein corresponding in size and shape to the transverse cross-section of punches 26a and 26b to permit movement thereof relative to these punches. The actuating cylinders 41 have moved pressure plate 42 and pressure transmitting rods 43 supported thereon upwardly an amount sucient to position the upper face of the clamping pressure plate 32 in the plane of the upper surfaces 27a and 27b of punches 26a and 26b. Two work pieces 31a and 31b which are to be drawn and shaped are disposedrespectively over punches 26a and 26b. Figure 3, therefore, illustrates the position and arrangement of the work pieces, tools and forming apparatus prior to the start of the actual pressing operation.

Figure 4 illustrates the relationship of the various elements after platen A has been advanced to effect the shaping of the work pieces.

As platen A moves downwardly in the shaping operation, the resilient die-forming face 25 of the female die forming element 24 engages the faces of the work pieces 31a and 31b and'applies pressure thereagainst to hold them lirmly against the upper surfaces of. punches 26a and 26b and to press their respective draw rings 33a and 33b irmly against the pressure plate 32 to clamp these draw rings between pressure plate 32 and the face 25 of female die forming element 24. Continued downward movement of the platen A advances punches 26a and 26b into the yieldable material of female die 24 to compress it, and since the material is laterally restrained by the walls 18 of frame 17, the compression thereof eiects a molding force upon the work pieces 31a and 311; whichstretches and draws such pieces and bends them into shaped contact with the side walls of punches 26a and 26b to effect parts conforming to the outlines of the punches.

In the drawing and shaping operation of work pieces 31a and 31b the pressure plate 32, backed by the pressure rods 43, reacts against the pressure applied by the female die 24 to the draw rings 33a and 33b of the work pieces 31a and 31b to develop a clamping pressure upon the draw rings, the amount of this pressure is determined bythe setting kof the pressure relief valve 67 associated with cylinders 41. This determined clamping pressure will be constant or uniform and remains so as clamping7 pressure plate 32 is backed toward bolster 36 by the advance of platen A and female die 24. In the retreating movement of pressure plate 32, rods 43 are forced downwardly thereby, guided by holes 71 in bolster 36, to transmit the force and movement of platen A to lower pressure plate 42 and effect movement of plungers 63 into their associated stationary cylinders 62. The regulated relief of pressure in cylinders 62 by relief valve 67 assures that a predetermined uniform presl sure is maintained uponr the draw rings. The constant determined pressure applied to the draw rings is'of an t tional presses.

amount suicient to maintain the metal thereof at and smooth as the drawing operation proceeds, but not of an amount that would hinder progressive withdrawal of the metal from between pressure plate 32 and face 25 of female die 24 in the stretching and forming operation. There is no strain set up in the draw rings such as would cause cracking or tearing to occur; rather the clamping pressure applied to the work pieces prevents wrinkles, crimps, or other objectionable folds appearing in the parts formed.

There has thus been provided a shaping and forming apparatus which is universal in its application, having complete flexibility as to` shape and size of part to be formed, which affords a construction wherein the punching means are relatively unrestricted as to location, which by reason of its simplicity is well adapted to production use, which will accommodate a number of punches, similar or dissimilar in conformation, for simultaneous working of a plurality of work pieces, which is adapted to cooperate with various size laterally restrained resilient female dies, and which effectively performs the forming operation to produce a part desirable in all respects. The, apparatus of the present invention requires no unduly expensive elements and is adapted to use With convenln achieving the desired results the present apparatus, wherein a minimum of elements are employed, utilizes a bolster, rectangular in shape and having a thickness which permits it to be supported solely at its edges in order that a larger working area be afforded and one having no dead, or unusable portions, which bolster effectively supports the punching means and has a construction permitting substantially universal location thereupon of punching means, and which further Veffectively guides pressure transmitting rods for cooperation with a flat pressure plate of simple design, whose thickness is relatively less than that of the bolster plate, and which pressure plate effectively cooperates with the resilient female die to apply a clamping pressure, of a predetermined amount and in a desirable manner to the work piece to the end that the finished flanged product will be free of wrinkles or other similar objectionable defects.

While certain preferred embodiments of the invention have been specifically disclosed, it is understood that the invention is not limited thereto as many variations will be readily apparent to those skilled in the art and the invention is to be given its broadest possible interpretation within the terms of the followingV claims.

l. Apparatus for shape-forming planar metallic sheets,

comprising a die-holder for mounting an open housing with a flexible compressible substance mounted therein having a planar, resilient die-forming face, a die-support of rectangular form having a multiplicity of rows of equally spaced holes, each successive row of holes being displaced one-half the center distance between the holes,

said rows of holes arranged substantially throughout the Y rsolely at its edges, an integral clamping means positioned in juxtaposition to said male die members having a multiplicity of openings for receiving said male die members and adapted with the latter to support work pieces in position to be formed, a plurality of reciprocable rods passing through certain of said holes in said diesupport to engage said clamping Vmeans with their upper extremities, and pressure means operative upon the lower extremities of said rods for applying pressure upon.

said clamping means, which pressure is directed in Vopposition to the pressure exerted, in the forming operation,

Vby said resilient die-forming face against the draw ring portions of said work'pieces interposed betweenrsaid resilient die-forming face and said clamping means to maintain an effective clamping pressure on said draw ring portions while said work pieces are formed.

2. Apparatus for shape-forming planar metallic sheets, comprising a die-holder for mounting a body of conformable, resilient material having a planar, resilient-dieforming face, a die-support of rectangular form having a multiplicity of rows VVof equally'spaced through holes arranged substantially*throughout the entire working area thereof and adapted to accommodate means permitting the readily removable mounting and in a variety of position-s of a plurality of rigid male die members for engagement by said die-forming face, means for supporting said die-support solely at its edges, a flat, integral clamping means positioned in juxtaposition to said male die icmbers having a multiplicity of openings therethrough for receiving said male die members, and adapted with the latter to support work pieces in position to be formed, a plurality of reciprocable rods passing through said holes in said die-support to engage said clamping means with their upper extremities, a pressure plate for supporting the lower extremities of said rods, and a plurality of actuating cylinders for applying pressure upon said pressure plate whereby said rods exert pressure upon said clamping means, which pressure is directed in opposition to the pressure exerted, in the forming operation, by

said resilient die-forming face again-st thedraw ring por- Y tions of said work pieces interposed between said dieforming face and said clamping means to maintain an effective clamping pressure on said draw ring portions while said work pieces are formed.

3. Shape-forming apparatus for use in conjunction with spaced, relatively movable platens, a die-holder carried by one of said platens for supporting a female die comprising a laterally restrained resilient flowable body having a planar, resilient die-forming face, a die support for t readily, removably supporting a number of rigid male die members, said die support having a multipli-city of rows of equally spaced holes, each successive row of hoes being displaced one-half the center distance between the holes, said rows adapted to accommodate means for removably mounting said plurality of rigid male die members and in various positions for engagement by said resilient face, pedestal means positioned on the other of said platens for supporting said die-support solely at its edges, a unitary clamping means positioned ladjacent said male die members having openings for accommodating said male die members and adapted with said male die members to support work pieces in position to be formed, a plurality of `reciprocable rods passing through -said holes to engage said clamping means with their upper extremities, a pressure plate 'for supporting the lower extremi-v ties of said rods, and a plurality of actuating cylinders supported by said other platen for moving said pressure plate to move said rods to exert pressure upon said clamping means, which pressure is directed in opposition to the pressure exerted, in the forming operation, by the female die against the draw ring portion of said work piece to apply an effective clamping pressure upon the draw ring portions during the forming operation.

4. Shape-forming apparatus for use with spaced, relatively movable platens, aVdie-holder carried by one of said platens for supporting a female die embodying a laterally restrained yieldable, compressible material having a resilient die-forming face, said female die comprising a housing having a flexible compressible substance mounted therein presenting a resilient die-forming face toward the other of said platens, a bolster plate of rectangular form having a multiplicity of rows of equally spaced holes, said rows being in staggered relationship, arranged substantially throughout the entire working area thereof and adapted to accommodate means for mounting and variously locating a plurality of rigid male die members in position to be engaged by said die-forming face, in position to be engaged by said resilient face, pedestal Ymembers carried byV said otherY of said platens for supporting the bolster plate solely at its edges and spaced from said latter platen, a movable unitary clamping means having openings for accommodating said male die-members, a plurality of reciprocable rods extending through Said holes in said bolster plate and engaging, with their upper extremities, the clamping means normally to position said clamping means with the upper planar face thereof in the plane of the planar faces of the male die members for the support of a plurality of work pieces above said male die members in position to be formed, a movable pressure platepositioned below said bolster plate and upon which pressure plate the lower extremities of said rods rest, a plurality of actuating cylinders disposed below said pressure plate and having an operative connection therewith whereby they may apply pressure on said rods to exert pressure upon 'said clamping means, which pressure is directed in opposition to the pressure exerted, in the forming operation, by the Illexible compressible 10 substance of said female die against the draw ring portions of said work pieces interposed between the female die and said clamping means to maintain an eiective pressure on said draw ring portions during the forming operation.

References Cited in the le of this patent UNITED STATES PATENTS 

